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Hello; I'm just getting started with the electric car scene. I've always been interested in making bikes, go karts, and my own vehicles for a while though. Although I've always planned on using small gas engines. Even though whenever I'd ride or walk through the city I'd curse everyone who drives by. With their loud cars and smelly exhaust. Well I've had enough so I'm going to rip the engine out of an old car and build my own EV to prove a point to everyone I can. That the technology is here, accessible, and relatively simple.

So enough about myself I've been batting around some ideas and settled on trying to have a go at EV using an old beef cakey US Electric three phase motor. I'm sure people are already slapping away at the keyboard about why that's stupid and getting a big DC motor would be better. But the thing is where I live you can get these big surplus three phase motors for dirt freaking cheap. Which is a good place to start for proving a point.

So to start if I'm using a three phase motor I'm going to have to convert the DC current from the batteries to three phase AC before it goes into the motor. So the way I understand it right now but I could be doing this wrong I'm not an electrical engineer. I have to first pass the current through an inverter to make it AC then pass it through a phase converter to make it three phase? Or are there inverters that can send it straight to three phase? I feel like that's a good place to start for now to clear somethings up.
 

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Not a dumb idea at all.

An inverter can take the DC from your batteries and output 3 phase AC right to the motor. It can also take 3 phase AC current FROM the motor and put it back into your batteries, which is called regenerative braking.

Most industrial 3 phase motors are totally enclosed, fan cooled. That's not a particularly good design for an EV application for two simple reasons: heat dissipation and weight. An EV involves generating a lot of peak power for short bursts, and a steady load during steady driving. To handle the peaks, you need the motor internals to be cooled very efficiently. A TEFC motor cools the internals indirectly by conduction from the internals to the finned exterior of the motor casing- great for keeping dirt and crap out of the motor internals in a dirty industrial environment.

The AC motors typically used in EVs fall into two categories: open drip proof (like my HPEVS AC50 in my Spitfire conversion), and forced liquid cooled (ie permanent magnet AC motors like the Rinehart etc.- I'd never even heard of one until I read about them here!).

An open drip proof motor is just like it sounds- it has openings and an internal fan driven off the motor shaft, that draws or pushes air through the internals of the motor for most efficient cooling. This helps a smaller motor put out more peak power for short periods without frying, though you can still fry it if you operate it at very low speeds and high powers for extended periods without an external fan driven by a separate motor.

To give you an idea, the nameplate power rating of my AC50 is only 15 hp- but it generates peaks to at least 50 hp and I run mine continuously on the highway at about 15 kW which is over 20.7 hp. It typically rises 20-40 degrees C above ambient air temperature without any kind of externally mounted blower or fan. You see the biggest spike in motor temperature (measured by a thermistor embedded in the motor windings) when you come off the highway to a stop- because the fan stops spinning the moment the motor stops turning.

Others here have adapted industrial inverters to work on DC feed power, using surplus AC induction motors. The Curtis controller that is usually paired with the HPEVS motors might also be used with ordinary AC induction motors, though an added shaft encoder may be required and it will also require the controller to be set up with the correct motor parameters. But I would imagine the biggest challenge would be voltage. Big AC induction motors are usually wired for high voltages- no lower than 208V AC typically. The Curtis controller has a maximum 144 V nominal battery voltage input, and though it's possible to generate a higher AC voltage from a lower battery voltage, that results in higher cost and some efficiency loss. So it would appear that you would need an industrial inverter and a quite high voltage battery pack- lots of smaller batteries in series. That has some hazards associated with it, as well as some challenges for charging from a low voltage source.

Best of luck- hope I've helped you understand things. Others more knowledgeable about the specifics will chime in and correct what I've said wrong.
 

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Yeah that helped alot, I'm glad there are inverters that can change over the current from DC straight to 3 phase AC. I'll start looking around for those if I can. The motor I was looking at on It's information plate had a 30HP rating. Which I'm going to assume it's probably it's peak horsepower. Which is that the max horsepower it puts out for a very short time right when the motor first turns on? Also the voltages on the side are 208, 230, and 460. Which those numbers correspond to the three phase right?
 

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Muttley likes your cool shady fox avatar!

Motor ratings like the 30 HP you have, are usually continuous duty. AC induction motors can provide up to 2 or 3 times rated torque at nominal voltage, but for shorter duty cycles, typically the inverse square of overload. So 25% at 2x and 10% at 3x. This means maybe 30 seconds at 2x and 10 seconds at 3x, which is adequate for short bursts. 30 HP is plenty big for an average size compact or mid-size car.

You can also overclock a motor to get higher speed, and even higher power if you also increase voltage. Thus if your 30 HP motor is connected for 240 VAC and is 4 pole (about 1700 RPM at 60 Hz), you can get 60 HP continuous by applying 480 VAC at 120 Hz and it will run at 3400 RPM. You need a battery pack of at least 500-600 VDC to get 480 VAC, and that can be rather dangerous and expensive, but you can still overclock a motor to get the higher speed at lower voltage if you don't mind a reduction in torque.

There are ways to boost lower battery voltages to much higher levels by using a DC-DC converter, but might be very expensive for the likes of 30 HP (22 kW). I have hacked a 1000 watt automotive inverter (12 or 24 VDC to 220 VAC) to access its internal 260-280 VDC supply for a 2 HP inverter driving a small motor on a lawn tractor.

Good luck with your conversion!
 

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If that motor is 30 horsepower continuous that's freaking awesome for being only like a 300$ surplus motor. Also thanks I made the avatar for other stuff. Anyway I cannot for the life of me figure out how to hell I'm going to power the damn thing though. Ive searched for hours for inverters, phase converters, inverter and phase converters. I cannot find anything that is like what I'm looking for. The only thing Ive been able to find are rotary phase converters which I'm sure as shit not going to be using.

I'm I doing something wrong or looking for the wrong thing? I'm feeling like powering this three phase motor will turn into an absolute task. But It's so much bang for the buck. I'm looking for a generic black box to turn my inverted AC to three phase lol. If what I'm getting from Moltenmetal is correct, there are inverters that can also make the current three phase while their at it? Also what exactly are DC/DC converters. I though they were just used for powering the car's standard 12v system. Are they meant to actually up the voltage from the batteries to power the motor?
 

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Your best bet may be to get a battery pack from a wrecked Chevy Volt, or possibly another EV or hybrid like a Prius. They are (I think) about 300 volts and should be able to connect directly to the DC bus of a 240 VAC inverter which will then power the motor. Here is an article with a tear-down video:
http://www.greencarreports.com/news/1093708_whats-inside-chevrolet-volt-battery-pack-and-drivetrain-video-teardown-shows-all


As for the DC-DC converters, there is a thread somewhere about my concept of making modules with about 48 VDC batteries and 5 kVA DC-DC converters which can be connected in series and parallel to get the voltage and current you need. I have a preliminary design for them but they are a long way from production (if ever). I estimate that the converter will cost about $200-$300 for 5 kVA, and batteries will cost anywhere from about $400 (for lead-acid) to $2000 (for LiFePO4). You may also need to factor in a BMS and a charger. So most serious EV conversions will require an investment of $5000 to $20,000 for batteries and associated components. Bare minimum might be about $2000 for a grocery-getter.
 

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Ill check out those volt batteries. Once I figure out the electric things about the motor I wanted to experiment with making my own batteries by connecting many NIHM cells. Ive used NIHM alot for things like airsoft. They seem really good with weight to electric output.
 

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I cannot for the life of my find any DC to 3 phase AC motor controllers for sale. Only ones people have made themselves. Which is way out of my current electronics experience.
 

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Hi
If you want to buy one you need to look up things like Curtis and Rinehart

http://curtisinstruments.com/?fuseaction=cProducts.dspProductCategory&catID=8

http://www.rinehartmotion.com/products.html

Get sat down before you look at the prices - especially on the Rinehart

That is the problem with AC systems

You can get industrial controllers - but you need to rework them for DC
Or you can get controllers for EV's - but they work with specific motors and still cost a lot

An AC motor/controller will be wimpy at $8000
Or superb at $18,000

My DC motor cost $100 and its controller cost $600 its a lot more powerful than the $8000 one (not as good as the $18,000 one)

That was scrounging old motor and making a controller from a kit
If I had bought new it would have been
$3000 for the motor and $1500 for the controller
Still a lot less than $8000 - and with about twice the power

AC is the way of the future - but it's a bit too expensive now
 

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Discussion Starter #11 (Edited)
God damn the AC one is about 900$ and another for freaking 2000$. But maybe that's not so bad If It's inverting to 3 phase and controlling all in the same box? So it saves me from having separate parts. The reason why I'm so dead set on these surplus three phase AC motors is when I was looking around the only other motors rated at up near 30hp like that were like 1000$+ DC motors. I'm not trying to build something nice. If I can just get the 300$ three phase motor running then I'm set. There has got to be some cheaper way. The only other motors I'm finding on ebay that compare in price to the 300$ three phase are weaker single phase DC ones.
 

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The first thing a VFD does is rectify the AC to DC, just like any other switching supply. You can run most switching supplies and VFDs directly on DC, and you may be able to connect the DC to a pair of the AC inputs if the bus link is not readily available. BUT many VFDs have phase loss detection or phase-modulated inrush control that may interfere with using it directly on DC.

I know you are experiencing sticker shock when you find a great bargain like a $300 30 HP motor, but the extra components to make it work on an EV are easily 10 times that. You might want to get some experience with AC motors, VFDs, batteries, and chargers, before delving too deeply into your conversion. You CAN run the 30 HP motor on a much smaller VFD, perhaps as small as 7.5 or 10 HP, which can be found for under $500. You also can build a "bad boy" voltage booster to run a 480 VAC VFD, and you could also run many 240 VAC VFDs from 220 VAC single phase. You could even mount the components in a car and use an extension cord to test drive it in your driveway, before investing in batteries.

There is someone who is selling some 7.5 HP VFDs for cheap, but I don't know what he wants for them or if they will work for you on DC:
http://bbs.homeshopmachinist.net/threads/67119-Need-480V-3Phase-from-240V-1Phase

I bought a 7.5 HP Toshiba VFD a couple years ago for under $100:



It appears to have a connection for the DC bus link, which is available on the DBR (Dynamic Braking Resistor) connections at the top:



You may also want to do a lot more studying and maybe start with a simpler, cheaper project such as I have been doing with my electric lawn tractor. Here is a video of a brief ride using a 2 HP 3 phase motor, 2 HP VFD, and a home-made 24V to 320V DC-DC converter running on two 12V batteries:


And this shows the VFD and motor powered from a 1000W 12V to 220 VAC inverter (which was about $50):
https://www.youtube.com/watch?v=kTsHYm5Y78U

I started a thread here which shows how I took apart a 24V 1500W inverter to access the internal 260 VDC which would work on the VFD inverter. If you feel overwhelmed and confused by the concepts presented here, a full DIY conversion, especially AC, may be unwise and unsafe, at least until you get more knowledge and experience.
 

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That helps alot, I'll definitely read up on VFD's . How come the VFD's have a horsepower rating? Also sticker shock is totally the term for that. I'm finding all these strong old three phase motors for such bargains It seems like it should be pretty straight forward and cheap to drive the pretty straight forward and cheap motor.

I don't know why those common motor controllers are so expensive but so help me I will find a way around. I'll probably have to start researching hobby circuitry. Another project I was thinking about doing was a DC electric gokart. But I don't have much time before I join the marines so I figure if I go I outta go hard.
 

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It's straightforward and cheap to drive a surplus 3 phase AC motor at a fixed speed- all you need is a cord, if you don't mind the inrush current...

To drive one at variable speed, even from a 3 ph AC supply, requires a big inverter, and that's expensive. To drive it from DC requires some hacking because this application represents a tiny fraction of the applications of such motors. But as has been mentioned, the first step in these inverters is a 3ph bridge rectifier to produce DC, so hacking, if a high enough voltage DC supply us available, may be possible. A good way to get dead, though, if you don't know what you're doing. Not for the ignorant or faint of heart. I just bought the finished articles, as hard as that was on me given what a cheapskate I've been my whole life, but it was a decision with higher survival value.

All electronic devices have power ratings, and all get more expensive as the current increases. With the current, all problems increase, but the biggest cost is the power transistors that switch the DC current on and off at high frequency to produce an AC waveform to drive the motor. Driving a high power DC motor at variable speed isn't easy, but it's far easier than the 3 phase AC problem and takes much less complexity and parts count to solve.
 

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I see, well that clearly is why the DC motors are so popular for EV. Although I'm not faint of heart and very careful around electricity I would have to learn a lot before I'd attempt hacking together something myself. I horribly messed up a circuit in HVAC class when I just tried to fudge it.

What a cruel irony that such affordable but powerful motors are so complex and expensive to drive well in an EV application. Although I suppose it isn't that difficult if you just throw money at it. But what kind of inventive spirit is that? I'm going to put all this in my notes, If I don't get to the project right away eventually I will get to it. EV is definitely the future for daily driving activities.

So the current's journey to the motor we're starting off with DC in the batteries. Which we then need to put through an inverter that pulses it making it into AC. Then we need to get that AC current into 3ph which would be 3 powered lines and a neutral? So couldn't we just split off from the one line into 4 lines and run the non neutral lines through some kind of AC/AC converter? And then into the motor?
 

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One thing to consider, regarding the cost of DIY EV components, is that they are for the most part lifetime investments with little additional maintenance and repair costs. An AC induction motor, particularly, should never need anything more than cleaning and bearing replacement or lubrication, whereas an ICE has many parts that can fail dramatically and expensively. A good VFD, especially one made for DIY EVs, is relatively easy to service, and usually might need only capacitor or IGBT replacement.

The only item that is subject to degradation and need for eventual replacement is the battery pack, and it's not all that bad if you consider the annual cost. A 20 kW-h LiFePO4 pack may be about $10,000 and will last 10 years, so $1000/year or less than $100/month. A 20 kW-h lead-acid pack may be as little as $2000, but will actually give you only about 10 kW-h, and may last only 3 years. So for a true 20 kW-h pack (requiring 40 kW-h of lead), it would be $4000 over three years or $1300/year. Plus, 40 kW-h of lead weighs about a ton, so you'd need a truck, and your energy usage will increase from about 250 W-h/mile to 500 W-h/mile.

However, it may be a reasonable option for a learning experience and an inexpensive way to get up and running quickly and cheaply. You can get 12V 35 A-h (420 W-h) SLA batteries from Harbor Freight for about $75 each. You can put 20 of them in series for 240 VDC which is enough for the DC bus link of an industrial VFD. So you can get an effective 4.2 kW-h pack good for maybe 15 miles per charge, for about $1500. The total weight will be about 400 pounds. Once you get everything else working, and before you seriously weaken the batteries, you may be able to sell them to someone for a similar project for, say, half the price, and you will only be out $750 for the experience.

As for the conversion of DC to AC, the three legs of a VFD inverter create three phases of AC, each at 120 degrees phase rotation, and there is no neutral (it's delta and not star). You could use three batteries and three automotive 24V to 220V inverters to get three phases of modified sine wave (rectangular wave) voltage, but you would need to hack the circuitry to synchronize them at 120 degrees, and make the output adjustable in frequency and voltage. You can run an induction motor on such non-PWM waveforms, but it is not very efficient and not practical for anything more than a few HP.
 
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